ELECTROCHEMICAL STUDIES WITH TIN ELECTRODES IN CITRIC-ACID SOLUTIONS

The electrochemical behaviour of tin in 0.5 M citric acid solution (pH=1.8) was studied by means of the potentiodynamic method. The E-I profiles show an anodic current peak associated with a dissolution of the metal and the formation of a passivating film, and two cathodic current peaks which are related to the reduction of soluble Sn(II) species and reduction of the film. During the potential sweep in the cathodic direction, an anodic current peak can be observed and is interpreted in terms of a reactivation process. The data suggest that the passivation of tin in this medium occurs by a dissolution-precipitation mechanism. Depending on the potential sweep rate, the process is controlled either by mass transport or by the solution resistance in the pores of the film. © 1990 Chapman and Hall Ltd.